Background: Hereditary angioedema (HAE) resulting from C1-inhibitor deficiency is characterized by attacks of subcutaneous and submucosal edema. Many factors have been presumed to induce edema. Our study analyzed these factors in a fairly large patient population. Methods: In the first stage of our study, we analyzed the data recorded by 92 subjects in their patient diaries over seven years. The second phase included 27 HAE patients, who had been completing the diary entry ‘Trigger factors’ every day for seven months whether or not they had experienced an attack. Results: During the initial stage, 91% of the subjects described some factor possibly related to the onset of an attack. They could identify a trigger factor – most commonly (21%) mental stress – in 30% of the 3176 attacks. We found a significant (p < 0.001) difference in the distribution of the trigger factors of the edematous attacks of different locations. The 27 participants of the second phase identified 882 potential trigger factors and recorded 365 attacks. Of these, 246 (67%) occurred on days when the patients identified a potential trigger factor. The likelihood of edema-formation associated with the latter was as follows: menstruation – 63%, infection – 38%, mental stress – 26%, physical exertion – 25%, meteorological changes – 21%, fatigue – 17%. Conclusion: This analysis of the trigger factors explored, for the first time, their potential role in inducing HAE attacks. Our findings might open new perspectives in extending the indications for edema-prophylaxis, and could contribute to a better understanding of the pathomechanism of HAE attacks.